1. Field of the Invention
The present invention relates to an improvement of a bidirectional differential clutch.
2. Description of the Prior Art
Japanese Patent Application Laid-open No. H9-25959 discloses a conventional bidirectional differential clutch which as a structure shown in a vertical sectional view of FIG. 8, and in a semi-sectional view of FIG. 9 taken along the line IX--IX in FIG. 8. A rotational shaft 1 is rotatably supported by bearings 13 and 14, and an input gear 2 is rotatable supported around an outer periphery of the rotational shaft 1 by a bearing 15 at a distance from the bearing 14. A plurality of sprags 8 are interposed between an outer peripheral surface of the rotational shaft 1 and an inner peripheral surface of the input gear 2. Each of the sprags 8 is interposed between a pocket portion of an outer holding member 6, which is fixed to the inner peripheral surface of the input gear 2, and a pocket portion of an inner holding member rotatably disposed around the outer periphery of the rotational shaft 1 through a bearing 16. A pin 10 is provided in the inner holding member 4 and is inserted into a notch 7 formed in the outer holding member 6. The inner holding member 4 is mounted inside the input gear 2 through a bearing 17. A friction plate 3 is rotatably mounted on an end of the inner holding member 4 and is pressed against a flange 4a of the inner holding member 4 by resiliency of a resilient member 5. The friction plate 3 is prevented from rotating by a peripheral case. As shown in FIG. 10, the inner holding member 4, which abuts the frictional plate 3 under pressure, generates a difference in speed with respect to the rotation of the input gear 2, and the inner holding member 4 relatively rotates leftward in the drawing until a stopper 10 abuts against an end of the outer holding member 6. With this relative rotation, each of the sprags 8 inclines. In this case, if the rotational shaft 1 rotates faster than the input gear 2, the sprag 8 rises and the rotational shaft 1 rotates idly. However, if the rotational shaft 1 rotates slower than the input gear 2, the sprag inclines so that the inner peripheral surface of the input gear 2 is connected to the outer peripheral surface of the rotational shaft 1, and the rotation of the input gear 2 is transmitted to the rotational shaft 1. That is, this bidirectional differential clutch transmits the rotational force of the input gear 2 to the rotational shaft 1 only when the input gear 2 rotates faster than the rotational shaft 1 regardless of the rotational direction.
An output gear 9 is spline-fitted around the outer periphery of the rotational shaft 1, and a gear at the side of vehicle wheels, for example, engages with the output gear 9 to transmits the rotational force to the vehicle wheels.
When the bidirectional differential clutch having such a structure is incorporated in a continuously variable transmission of an automobile, for example, in a state where a tension force of a belt of the continuously variable transmission can not be released at the time of switching of the running direction of the automobile between a forward direction and a rearward direction, when the bidirectional differential clutch is to be rotated in the reverse direction after the bidirectional differential clutch rotated in the normal direction and stopped, the sprags 8 can not incline in the reverse direction if a rotational speed ratio of the input gear 2 to the rotational shaft 1 is one or less. Therefore, a problem is caused that it is impossible to rotate in the reverse direction.